GALVANISING AND PAINTING
GALVANISING

All our products have a galvanised finish, which is applied to improve steel corrosion resistance (and also that of iron alloys) by means of a thin surface coating. This type of solution is very effective also in highly corrosive environments (See Table 1).

TABLE 1
Corrosivity of atmospheres and corrosion rate of zinc.
Corrosivity category
Environments
Corrosion rate of zinc (µm/year)
C1 Interior: Dry 0,1
C2 Interior: Ocasional condensation. 0,1 to 0,7
Exterior: Rural, inside the country.
C3 Interior: High humidity, air slightly polluted. 0,7 to 2
Exterior: Urban, inside the country coastal or low salinity.
C4 Interior: Pools, chemical plants, etc. 2 to 4
Exterior: Industrial on the outside of country or coastal city.
C5 Exterior: Industrial wet or coastal high salinity. 4 to 8

El Unprotected steel has an average useful life of only two years before its functionality or structural integrity are affected. However, galvanised coatings applied at galvanising plants last at least ten years without the need for any maintenance, even in the worst atmospheric conditions.

The basic standard specifying the requirements to be met by galvanised coatings applied at hot-dip galvanising plants is the Spanish and international Standard UNE EN ISO 1461:2009, "Hot-dip galvanised coatings on products finished in iron and steel".

The galvanising process consists of applying a zinc coating to the iron or steel parts and products by immersing them in a zinc bath smelted at 450ºC.

During their immersion in molten zinc, a diffusion reaction occurs between the zinc and the steel, which results in the formation of different layers of zinc-iron alloys.

When the materials are removed from the zinc bath, these alloy layers are covered by an outer layer of pure metal, which, as a whole, give the steel an excellent level of resistance to corrosion.

The galvanising reaction is only produced if the material surfaces are chemically clean, which is why the latter must previously undergo a surface preparation process.

Therefore, the stages we go through at our plant to achieve a correct surface finish are the following:

1- Hanging the parts

2- Degreasing

3-Stripping

4- Fluxing

5- Galvanising

6- Unhanging the parts

7- Finishing touches

Our   galvanising vat measures 12.5 m long x   2.5 m deep x 1.5 m wide, measurements that permit us to galvanise materials of different lengths and with hardly any limitations.

After galvanising the parts, we subject them to an inspection process to check their final appearance as well as the thickness of the coating obtained, to ensure they comply with Standard UNE EN ISO 1461:2009.

(See Table 2).
TABLE 2

Minimum thickness of the coating on saples without centrifugation.
UNE EN ISO 1461:2009.

Workpiece thickness (mm)
Local minimum thickness coating (µm)
Minimum average coating thickness (µm)
Steel ≥ 6mm. 70 85
Steel ≥ 3mm. up to < 6 mm. 55 70
Steel ≥ 1,5mm. up to < 3mm. 45 55
Steel< 1,5 mm. 35 45
Castings ≥ 6mm. 70 80
Steel< 6mm. 60 70
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